Scientists develop sub-microscopic probes to measure cell chemistry

August 21, 1995

CHICAGO—University of Michigan chemists have developed a series of fiber-optic biochemical probes” each 1,000 times finer than a human hair” that can measure specific chemical properties within a living cell.

Probes are now available to measure cell acidity or pH, as well as the concentration of dissolved oxygen, glucose, calcium, potassium and sodium ions, according to Raoul Kopelman—the Kasimir Fajans Professor of Chemistry, Physics and Applied Physics at the University of Michigan—who developed the basic probe fabrication technology in the early 1990s.

“The probes are five to 50 times smaller than a typical red blood cell, so they do not damage cells in any way during the measurement process,” Kopelman said. “Accurate measurements can be obtained in as little as one-hundredth of a second, which makes it possible to monitor processes inside the cell as they occur. The probes are as easy to use as conventional sensors and require much smaller sample volumes.”

Kopelman discussed the latest developments in biochemical probe technology during a presentation and press conference at the American Chemical Society Meeting held here Aug. 20-24.

Potential biological applications for the probes in research and medicine are extensive, according to Kopelman. They include testing the effects of new drugs on single cell—which could reduce the need for animal testing—monitoring embryos for birth defects, gene sequence identification, and detection of individual cells or even single molecules within a sample.

“Not only can this sensor measure the chemical properties of cells, it can monitor chemical changes while they occur within cells as they respond to external changes in their environment and to internal changes occurring within embryonic cells as an organism develops,” Kopelman said.

A nanotechnology manufacturing technique called near field photopolymerization makes the probe possible. The process begins when researchers shine a beam of light into one end of an optical fiber whose other end has been pulled to form a fine tip, which is coated with aluminum. The light emerges from a small opening in the fiber tip, which rests in a solution of molecules called monomers. The light induces a chemical reaction between the monomers and the molecules on the end of the tip forming a polymer plug in the tip’s hole.

The polymerized tip is then embedded in the cell sample and laser light is introduced to make the tip fluoresce or glow like a firefly. The color and intensity of emitted light indicate the concentration of the material being measured.

“The predetermined chemical composition of the probe tip determines whether it is sensitive to oxygen, calcium ions, sodium ions or pH,” Kopelman explained. “The glucose probe, which may prove useful in diabetes research and treatment, contains enzymes that metabolize glucose molecules with the aid of oxygen molecules.”

The research was funded by the U.S. Department of Energy and the National Institutes of Health. The U-M has received two patents for the sensing probes.

Prof. Kopelman’s presentation before the Materials Chemistry Secretariat at the ACS Meeting will take place at 9 a.m. on Tuesday, Aug. 22 in McCormick Place North, room 133, level one. A press conference is scheduled for 11 a.m. on Wednesday, Aug. 23 in the Hyatt Regency’s Water Tower Room.


Related Links: